1. Field of the Invention
The present invention is directed towards the production and operation of micromechanical structures such as sensors having a layered structure. More specifically, the present invention is directed towards micromechanical components having a layered structure wherein adjacent layers have a tendency to stick or adhere to one another.
2. Description of the Prior Art
A basic problem in the production and especially in the operation of micromechanical structures is the sticking of the movable parts to oppositely situated surfaces in the case of large deflections. Very strong, short-range intermolecular forces such as the Van-der-Waals force and hydrogen-bridge bonds result therefore an inseparable joint between the deflected micromechanical structure and the oppositely situated surface, making the component unusable. This problem occurs, in particular, in the case of very sensitive acceleration sensors which have a correspondingly pliantly suspended material part and in which adherence of the micromechanical structure to the fixed part may arise during the occurrence of accelerations. In addition, the problem occurs that a short circuit may arise between a movable part used as electrode and an electrode disposed opposite said part, which also leads to the destruction of the component.
Methods have been developed for the production of micromechanical structures which avoid the adherence of moving structures. Said methods do not, however, solve the problem that said adherence may occur even after production, that is to say during the operation of the component. In order to avoid sticking during the operation, a number of small raised sections directed toward the oppositely situated surface can be produced in the layer structure in which the moving micromechanical part is formed. The contact area is consequently kept very small in the case of a collision between the oppositely situated surfaces. In order to produce said structure, an additional photographic procedure and an isotropic and (additional) etching step is required. In these method steps, recesses are produced in a sacrificial layer (i.e, an auxiliary layer to be removed subsequently). The structural layer is then deposited conformally onto this sacrificial layer, so that the recesses in the sacrificial layer remain as raised sections of the structural layer when the sacrificial layer is removed. This method is shown in FIGS. 2 to 5. FIG. 2 shows an intermediate product of the component in cross section, in which a sacrificial layer 11 and, on top thereof, a mask 12 having an opening 13 are applied to a substrate 10 in the region of the recess to be produced. FIG. 3 shows how a recess is etched in the sacrificial layer 11 through the opening 13. After the removal of the mask 12, the structural layer 20 provided for the movable part is applied with a uniform thickness (see FIG. 4). After the removal of the auxiliary layer 11, the structure shown in FIG. 5 is obtained, in which structure the structural layer 20 has a raised section on the side adjacent to the substrate 10. The structural layer 20 can be patterned according to the sensor to be produced. This method does not make it possible to produce raised sections on the structural layer which are sufficiently high and pointed. The dimensions of the elevations are in fact limited in the downward direction by the resolving power of the photographic procedure used in the process and the subsequent wet-chemical etching, so that narrow spikes cannot be produced. For extremely miniaturized micromechanical components, this method of avoiding sticking is therefore usable only to a very limited extent. The disadvantage is that an electrically conducting contact occurs between the faces in the case of contact between the movable part and the substrate surface and if electrodes are provided the electrically conducting contact is also not thereby eliminated.